Plurality of different size metal layers for a pad structure

ABSTRACT

Methods and apparatus are disclosed for manufacturing metal contacts under ground-up contact pads within a device. A device may comprise a bottom metal layer with a bottom metal contact, a top metal layer with a top metal contact, and a plurality of middle metal layers. Any given metal layer of the plurality of middle metal layers comprises a metal contact, the metal contact is substantially vertically below the top metal contact, substantially vertically above the bottom metal contact, and substantially vertically above a metal contact in any metal layer that is below the given metal layer. The metal contacts may be of various and different shapes. All the metal contacts in the plurality of middle metal layers and the bottom metal contact may be smaller than the top metal contact, therefore occupying less area and saving more area for other functions such as device routing.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation and claims the benefit of U.S.application Ser. No. 13/787,673, filed on Mar. 6, 2013, entitled “Methodand Apparatus for Packaging Pad Structure,” which application is herebyincorporated herein by reference in its entirety.

BACKGROUND

Since the invention of the integrated circuit (IC), the semiconductorindustry has experienced rapid growth due to continuous improvements inthe integration density of various electronic components (i.e.,transistors, diodes, resistors, capacitors, etc.). For the most part,this improvement in integration density has come from repeatedreductions in minimum feature size, which allows more components to beintegrated into a given area. These smaller electronic components alsorequire smaller packages that utilize less area than previous packages.Some smaller types of packages for semiconductor devices include quadflat pack (QFP), pin grid array (PGA), ball grid array (BGA), flip chips(FC), three dimensional integrated circuits (3DIC), wafer level packages(WLP), wafer-level chip scale packages (WLCSP), and package on package(PoP) devices.

In a typical manufacturing process, active and passive devices may bemade within a substrate, and connected by interconnect structures suchas metal contacts formed on metallization layers and dielectric layers.Contact pads are formed above the metallization layers to makeconnections to packages. Typically, redistribution layer (RDL) orpost-passivation interconnect (PPI) may be used to fan out wires forcontact pads, followed by the formation of UBM layers connected to RDLsand solder balls on the UBM layers to establish electrical contactsbetween contact pads of a chip such as input/output pads and thesubstrate or lead frame of the package.

Ground-up contact pads can be used for packages such as flip-chippackages. Ground-up contact pads require no redistribution layer,instead UBM layers and solder balls are placed on ground-up contact padsdirectly, and ground-up contact pads are connected to metal contactswithin a plurality of metal layers of the chip. However, conventionalinterconnects for ground-up contact pads occupy large areas of metallayers, which ultimately limit the areas available on metal layers forother functions such as device routing. Methods and apparatus are neededfor reducing metal layer areas occupied by metal contacts underground-up contact pads, and at the same time, increasing the areaavailable for other purposes such as device routing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an embodiment of a ground-up contact pad of a deviceabove a plurality of metal contacts;

FIGS. 2(a)-2(e) illustrate an embodiment of the formation of a pluralityof metal contacts under a ground-up contact pad;

FIGS. 3(a)-3(e) illustrate various embodiments of the formation of aplurality of metal contacts under a ground-up contact pad; and

FIGS. 4(a)-4(c) illustrate further additional embodiments of theformation of a plurality of metal contacts under a ground-up contactpad.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that theembodiments of the present disclosure provide many applicable conceptsthat can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed are merely illustrative of specific waysto make and use the disclosure, and do not limit the scope of thedisclosure.

Methods and apparatus are disclosed for manufacturing metal contactsunder ground-up contact pads within a device. A device may comprise abottom metal layer with a bottom metal contact, a top metal layer with atop metal contact, and a plurality of middle metal layers. Any givenmetal layer of the plurality of middle metal layers comprises a metalcontact, the metal contact is substantially vertically below the topmetal contact, substantially vertically above the bottom metal contact,and substantially vertically above a metal contact in any metal layerthat is below the given metal layer. The metal contacts may be ofvarious and different shapes. All the metal contacts in the plurality ofmiddle metal layers and the bottom metal contact may be smaller than thetop metal contact, therefore occupying less area and saving more areafor other functions such as device routing. The so formed metal contactsmay also provide lower metal sheet resistance and reduced IR drop, withincreased yield and reliability.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, or connected or coupled to the other element orlayer or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to” or “directly coupled to” another element or layer, thereare no intervening elements or layers present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present inventive concept.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “above” or “below” can encompassboth an orientation of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,”—when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. It shouldbe appreciated that the following figures are not drawn to scale;rather, these figures are merely intended for illustration.

A device 100 is illustrated in FIG. 1, wherein the device 100 comprisesa ground-up contact pad 501. The device 100 comprises a substrate 201,which may contain active and passive devices, such as a transistor 203,an isolation area 205 which may be a shallow trench isolation area(STI), and another passive device 207. A bottom metal layer 101 isseparated by an inter-layer dielectric (ILD) layer 111 from thesubstrate 201. The bottom metal layer 101 comprises a plurality ofbottom metal contacts 301. The top metal layer is a term known to thosewith ordinary skill in the art. The metal layer 107 is the top metallayer of a chip so that there is no other metal layer above the metallayer 107 within the chip. The top metal layer 107 comprises a pluralityof top metal contacts 307. The metal layers 103 and 105 are the middlemetal layers between the bottom metal layer 101 and the top metal layer107, comprising the middle metal contacts 303 and 305 respectively.Metal contacts 301, 303, 305, and 307 may be connected by vias such as401, 403, and 405, respectively. The bottom metal layer 101, the topmetal layer 107, and the middle metal layers 103 and 105 are separatedby a plurality of inter-metal dielectric layers (IMD) 113, 115, and 117,respectively. In an embodiment there may be more than four layers ofmetallization separated from the substrate 201 by at least one ILD, butthe precise number of metallization layers is dependent upon the designof the device 100.

The contact pad 501 may be formed on the surface of the top metal layer107 in contact with the top metal contact 307. A passivation layer 502may be formed on the top metal layer 107 with a first opening to exposethe contact pad 501. A polymer layer 504 may be formed above thepassivation layer 502, with a second opening contained within the firstopening to expose the contact pad 501. An UBM layer 503 may be formedwithin the second opening of the polymer layer 504, and in contact withthe contact pad 501. Furthermore, a solder ball 507 may be placed on theUBM layer 503 to connect the contact pad 501 to other packagingmaterials.

The contact pad 501 is connected to the UBM layer 503 directly without aredistribution layer, and it is further placed on a plurality of metalcontacts 301, 303, 305, and 307. The contact pad 501 is a so-calledground-up contact pad. Such ground-up contact pads may be used forpackages such as flip-chip packages. However, conventional ground-upcontact pads have metal contacts under the ground-up contact padoccupying large areas of metal layers, which ultimately limit the areasavailable on metal layers for other functions such as device routing.The embodiment of the ground-up contact pad 501 shown in FIG. 1 has aplurality of metal contacts 301, 303, 305, and 307 occupying less areain the metal layers. More details of each component may be describedbelow, while more details of the metal contacts 301, 303, 305, and 307will be shown in FIGS. 2(a)-2(e), FIGS. 3(a)-3(e), and FIGS. 4(a)-4(c).

The substrate 201 may comprise bulk silicon, doped or undoped, or anactive layer of a silicon-on-insulator (SOI) substrate. Generally, anSOI substrate comprises a layer of a semiconductor material such assilicon, germanium, silicon germanium, SOI, silicon germanium oninsulator (SGOI), or combinations thereof. Other substrates that may beused include multi-layered substrates, gradient substrates, or hybridorientation substrates.

The substrate 201 may comprise active devices such as transistors 203,where a plurality of drain and source regions of transistors are formedwithin the substrate. Shallow trench isolation (STI) regions 205 andother passive devices 207 may be formed in substrate 201 as well. As oneof ordinary skill in the art will recognize, a wide variety of otherdevices such as transistors, resistors, inductors and the like may beused to generate the desired structural and functional requirements ofthe design. The substrate 201 does not need to contain all of thedifferent kinds of devices. The substrate 201 may contain only one kindof devices such as transistors 203. The transistors 203, the STI 205,and the passive device 207 may be formed using any suitable methodseither within or else on the surface of the substrate 201.

The ILD layer 111 may be formed on the substrate 201, covering the gateof the transistors and other devices. The ILD layer 111 may be made ofone or more suitable dielectric materials such as silicon oxide, siliconnitride, low-k dielectrics such as carbon doped oxides, extremely low-kdielectrics such as porous carbon doped silicon dioxide, the like, or acombination thereof. The ILD layer 111 may be formed through a processsuch as chemical vapor deposition (CVD), although any suitable processmay be utilized.

The bottom metal layer 101 may be formed over the ILD layer 111,comprising a plurality of bottom metal contacts 301 connected to thedevices within the substrate 201 by vias through the ILD layer 111. Amiddle metal layer 103 may be formed above the bottom metal layer 101separated by an inter-metal dielectric (IMD) layer 113, and a pluralityof metal contacts 303 may be located in the metal layer 103. Those metalcontacts 303 may be called middle metal contacts since they arecontained in a middle metal layer. Similarly, an additional middle metallayer 105 comprising middle metal contacts 305, and the top metal layer107 comprising top metal contacts 307 may be formed above the middlemetal layer 103 and separated by the IMD layer 115 and 117,respectively.

The bottom metal contacts 301, middle metal contacts 303, 305, and topmetal contacts 307 within various metal layers 101, 103, 105, and 107are connected by a plurality of vias 401, 403, and 405. The bottom metalcontacts 301, middle metal contacts 303, 305, and top metal contacts 307may be made with aluminum (Al), copper (Cu), titanium (Ti), or otherelectrically conductive material.

The number of metal layers 101, 103, 105, and 107, the number of IMDlayers 113, 115, and 117, the number of vias 401, 403, and 405, and thenumber of metal contacts 301, 303, 305, and 307 are only forillustrative purposes and are not limiting. There could be other numberof layers that is more or less than the four metal layers. There may beother number of IMD layers, and other number of vias, different fromthose shown in FIG. 1.

Each layer, such as the ILD layer 111, or the IMD layers 113, 115, and117 may be deposited by methods including chemical vapor deposition(CVD) process, or plasma enhanced CVD (PECVD). The IMD layers 113, 115,and 117 are commonly known in the art as being the dielectric layers forforming metal contacts and vias therein. The IMD layers 113, 115, and117 may have a thickness ranging from perhaps 500 Å to 30,000 Å. Thepatterning of the layers may be done using a damascene process or a dualdamascene process. Damascene means formation of a patterned layerimbedded in another layer such that the top surfaces of the two layersare coplanar. An IMD is deposited either on a substrate, or on top ofanother existing layer of metal. Once the IMD is deposited, portions ofthe IMD may be etched away to form recessed features, such as trenchesand vias, which can be filled with conductive material to connectdifferent regions of the chip and accommodate the conductive lines. Adamascene process which creates either only trenches or vias is known asa single damascene process. A damascene process which creates bothtrenches and vias at once is known as a dual damascene process.

A conductive layer may be formed as the contact pad 501 on a surface ofa top metal contact 307 within the top metal layer 107. The contact pad501 may be made with aluminum (Al), copper (Cu), tin (Sn), nickel (Ni),gold (Au), silver (Ag), or other electrically conductive material. Thedeposition of the contact pad 501 may use an electrolytic plating,sputtering, PVD, or electroless plating process. The size, shape, andlocation of the contact pad 501 are only for illustration purposes andare not limiting. The contact pad 501 may be formed to have a thicknessof between about 0.5 μm and about 4 μm, such as about 1.45 μm. There maybe a plurality of contact pads for the device 100, which are not shown.

The passivation layer 502 may be formed over the top metal layer 107 forstructural support and physical isolation. The passivation layer 502 canbe made with silicon nitride (SiN), silicon dioxide (SiO₂), siliconoxynitride (SiON), or other insulating material. An opening of thepassivation layer 502 may be made by removing a portion of thepassivation layer 502 using a mask-defined photoresist etching processto expose the contact pad 501. The size, shape, and location of theopening made are only for illustration purposes and are not limiting.The passivation layer 502 may be formed through a process such aschemical vapor deposition (CVD), although any suitable process may beutilized, and may have a thickness between about 0.5 μm and about 5 μm,such as about 9.25 KÅ.

A dielectric layer such as a polymer layer 504 may be formed over thepassivation layer. The dielectric layer may be formed of a polymer, suchas an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO),and the like, although other relatively soft, often organic, dielectricmaterials can also be used. Formation methods include spin coating orother commonly used methods. The thickness of the polymer layer 504 maybe between about 5 μm and about 30 μm, for example. Alternatively, thedielectric layer 504 may be an oxide layer or a nitride layer. Anopening of the dielectric layer 504 may be made by removing a portion ofthe dielectric layer 504 using a mask-defined photoresist etchingprocess to expose the contact pad 501.

The UBM layer 503 may be formed in electrical contact with the contactpad 501 within the opening of the dielectric layer 504. The UBM layer503 may comprise a layer of conductive material, such as a layer oftitanium, or a layer of nickel. The UBM layer 503 may comprise multiplesub-layers, not shown. One of ordinary skill in the art will recognizethat there are many suitable arrangements of materials and layers, suchas an arrangement of chrome/chrome-copper alloy/copper/gold, anarrangement of titanium/titanium tungsten/copper, or an arrangement ofcopper/nickel/gold, or any multiple layers made of materials such astitanium (Ti), tantalum (Ta), tantalum nitride (TaN), nickel (Ni), orcopper (Cu), that are suitable for the formation of the UBM layer 503.Any suitable materials or layers of material that may be used for theUBM layer 503 are fully intended to be included within the scope of thecurrent embodiments. The UBM layer 503 may be created using processessuch as sputtering, or evaporation, depending upon the desiredmaterials. The UBM layer 503 may be formed to have a thickness ofbetween about 0.01 μm and about 10 μm, such as about 5 μm.

A solder ball or bump 507 may be placed on the UBM pad 503. Solder bumpsare widely used to form electrical interconnect in flip chip technologyor other types of technologies for IC packaging. Various sizes of solderballs or bumps are in use. A solder ball of a diameter size around 350μm to 500 μm may be called a package bump and used to connect a deviceto a printed circuit board (PCB). A solder bump of a diameter sizearound 50 μm to 150 μm may be called a flip-chip bump and used toconnect a device to a package substrate. The sizes of different solderballs or bumps are described for illustration purpose only and are notlimiting. With the continuous reduction of feature sizes and packagesizes, the sizes in embodiments may become smaller than the onesdescribed above. On the other hand, the solder ball 507 may be of abigger size such as a size of a flip-chip bump or a package bump aswell, depending on the particular applications of interest.Alternatively, connectors other than a solder ball may be placed abovethe UBM pad 503 to make electrical connections.

The solder ball 507 may be a solder ball comprising an electricallyconductive solder material, e.g., Sn, Ni, Au, Ag, Cu, bismuthinite (Bi)and alloys thereof, or combinations of other electrically conductivematerial. For example, the solder ball 507 may be a Cu/SnAg solder ball.Alternatively, a copper bump instead of a solder ball may be used as thesolder ball 507.

More details of the plurality of metal contacts 301, 303, 305, and 307under the ground-up contact pad 501 of FIG. 1 are illustrated in FIGS.2(a)-2(e). Some general terms may be described first and demonstrated inFIGS. 2(a)-2(c). An embodiment of the metal contacts 301, 303, 305, and307 may be shown in FIGS. 2(d)-2(e) in cross-section view and in topview.

As illustrated in FIG. 2(a) in top view, a metal contact 605 at onemetal layer is above another metal contact 603 at another metal layerwhen the metal layer containing the metal contact 605 is above the metallayer containing the metal contact 603. Alternatively, the metal contact605 may be the contact pad 501 shown in FIG. 1, and the metal contact603 may be any metal contact of FIG. 1.

A metal layer is said to be below or above another metal layer based ontheir relative physical position in the layout layers of the chip. Forexample, as shown in FIG. 1, the metal layer 107 is the top metal layerso that there is no other metal layer above the top metal layer 107within the chip. The top metal layer 107 is above all other metal layers101, 103, and 105. The bottom metal layer 101 is below all other metallayers 103, 105, and 107. The middle metal layer 105 is above the middlemetal layer 103. By a same idea, the contact pad 501 is above all themetal layers.

Two metal layers are adjacent if there is no other metal layer betweenthe two metal layers. For example, as shown in FIG. 1, the middle metallayer 103 is adjacent to the middle metal layer 105, and also adjacentto the bottom metal layer 101. For two adjacent metal layers, the one atthe upper layer is said to be the next above layer of the lower layer.For example, the metal layer 105 is the next above layer of the metallayer 103, and the top metal layer 107 is the next above layer of themetal layer 105. Similarly, the one at the lower layer is said to be atthe next below layer of the upper layer. For example, the metal layer103 is the next below layer of the metal layer 105, and the metal layer105 is the next below layer of the top metal layer 107.

The metal layer containing the metal contact 605 may be any given metallayer of the plurality of middle metal layers 103 or 105 in FIG. 1, orthe top metal layer 107 in FIG. 1. The metal layer containing the metalcontact 603 may be any layer below the given metal layer containing themetal contact 605, such as the middle metal layer 103 or 105, or thebottom metal layer 101 in FIG. 1. For example, when the given metallayer containing the metal contact 605 is the top metal layer 107, thenthe metal layer containing the metal contact 603 may be any of themiddle metal layer 103 or 105, or the bottom metal layer 101.Alternatively, when the given metal layer containing the metal contact605 is the middle metal layer 105, then the metal layer containing themetal contact 603 may be the middle metal layer 103, or the bottom metallayer 101. On the other hand, when the given metal layer containing themetal contact 605 is the middle metal layer 103, then the metal layercontaining the metal contact 603 may be the bottom metal layer 101,since the bottom metal layer 101 is the only metal layer below themiddle metal layer 103.

As shown in FIG. 2(a), the area 6051 is the projected image of the metalcontact 605 projected to the metal layer containing the metal contact603, sometimes it is said to be the projection of the metal contact 605onto the metal layer containing the metal contact 603. The metal contact605 is substantially vertically above the metal contact 603 if the metalcontact 603 is all or substantially contained within the projected image6051. Similarly, the metal contact 603 is substantially vertically belowthe metal contact 605 if the metal contact 603 is all or substantiallycontained within the projected image 6051.

The two metal contacts 603 and 605 may be of a similar shape. Forexample, the two metal contacts 605 and 603 shown in FIG. 2(a) are of arectangle shape. Along the four sides of a rectangle, there is a gap631, 633, 635, and 637 between each side of the projected image 6051 andeach side of the metal contact 603. The gaps 631, 633, 635, and 637 areall shown as bigger than 0 in FIG. 2(a). When the gaps 631, 633, 635,and 637 are non-zero around each side, the metal contact 603 is said tobe strictly smaller than the metal contact 605, and the metal contact605 is said to be strictly bigger than the metal contact 603. The metalcontact 605 and the metal contact 603 may be of other shapes, such as acircle, an octagon, a square, an elongated hexagon with two trapezoidson opposite ends of the elongated hexagon, an oval, or a diamond, in topviews.

Furthermore, the metal contacts 605 and 603 may be of different shapes.For example, the metal contact 605 may be a rectangle and the metalcontact 603 may be a circle as shown in FIG. 2(b). The gaps may bedefined around the four sides of the projected image 6051 of the metalcontact 605, as the gaps 631, 633, 635, and 637 shown in FIG. 2(b). Whenthe gaps are non-zero around each side, the metal contact 603 is said tobe strictly smaller than the metal contact 605, and the metal contact605 is said to be strictly bigger than the metal contact 603.

On the other hand, when the gap between an edge of the projected image6051 and a corresponding edge of the metal contact 603 is substantiallyclose to 0, then the metal contact 605 may not be strictly larger thanthe metal contact 603. FIG. 2(c) illustrates an example where the gapsbetween the edges of the projected image 6051 and the edges of the metalcontact 603 are close to 0 on all sides. In this case, it is called thatthe metal contact 603 is substantially overlapped with the projectedimage of the metal contact 605 projected to the metal layer containingthe metal contact 603, or simply that the metal contact 603 issubstantially overlapped with the metal contact 605 at different layers,or the metal contacts 603 and 605 are substantially overlapped atdifferent layers.

In more general terms, when the metal contacts 605 and 603 are of anyconvex shapes, the metal contact 605 is substantially vertically abovethe metal contact 603 when the metal contact 603 is contained within theprojected image 6051 of the metal contact 605 at the metal layercontaining the metal contact 603. The metal contact 605 is strictlylarger than the metal contact 603 if there is a non-zero distance alongeach point of the perimeter of the projected image 6051 to thecorresponding point of the perimeter of the metal contact 603.

Based on the illustrations in FIGS. 2(a)-2(c), an embodiment of themetal contacts 301, 303, 305, and 307 under the ground-up contact pad501 of FIG. 1 are shown in FIGS. 2(d)-2(e) and described below.

FIG. 2(d) illustrates a top view of the contact pad 501, the top metalcontact 307, the bottom metal contact 301, and the middle metal contacts305 and 303 within the middle metal layers 105 and 103. The contact pad501 is substantially vertically above the top metal contact 307, and allother metal contacts 305, 303, and 301. The top metal contact 307 issubstantially vertically above the metal contacts 305, 303, and 301,among which the metal contact 305 is said to be substantially verticallynext below the top metal contact 307. The metal contact 305 issubstantially vertically above the metal contacts 303 and 301, amongwhich the metal contact 303 is substantially vertically next below themetal contact 305. Finally, the metal contact 303 is substantiallyvertically above the bottom metal contact 301, and the bottom metalcontact 301 is also substantially vertically next below metal contact ofthe metal contact 303. In general, a metal contact A has a substantiallyvertically next below metal contact B if the metal contact A is in ametal layer one layer above the metal layer containing the metal contactB, and the metal contact A is substantially vertically above the metalcontact B.

In more general terms, when there is a plurality of middle metal layersabove the bottom metal layer 101 and below the top metal layer 107, forany given metal layer of the plurality of middle metal layers, there isa metal contact contained within the given metal layer, which may becalled a middle metal contact. For example, as shown in FIG. 1, if thegiven metal layer is the layer 105 of the plurality of middle metallayers, the metal contact contained within the given metal layer 105 isthe metal contact 305. Furthermore, the metal contact in the given metallayer of the plurality of middle metal layers is substantiallyvertically below the top metal contact and substantially verticallyabove the bottom metal contact. For example, the metal contact 305 inthe given metal layer 105 is substantially vertically below the topmetal contact 307 and substantially vertically above the bottom metalcontact 301. In addition, the metal contact in the given metal layer ofthe plurality of middle metal layers is substantially vertically above ametal contact in any metal layer that is below the given metal layer.For example, the metal contact 305 in the given metal layer 105 issubstantially vertically above a metal contact in any metal layers thatis below the given metal layer 105, which is the metal contact 303 inthe metal layer 103.

As illustrated in FIG. 2(d), the top metal contact 307 is substantiallyoverlapped with the projected image of the contact pad 501 projectedonto the top metal layer. It may be advantageous to have the top metalcontact 307 substantially overlapped with the projected image of thecontact pad 501 projected onto the top metal layer, because in this waythe top metal contact 307 can provide a strong support to the contactpad 501 without occupying too much area. If the top metal contact 307 isstrictly smaller than the contact pad 501, the top metal contact 307 maynot be able to provide a strong support for the contact pad 501.Furthermore, the metal contacts 305, 303, and 301 are all substantiallyoverlapped at different layers. The gaps at each layer such as the gaps351, 353, 355, and 357 around the middle metal contact 305, the gaps331, 333, 335, and 337 around the middle metal contact 303, 311, 313,315, and 317 around the middle metal contact 301, are the gaps comparedto the projected image of the top metal contact 307 projected to thecorresponding metal layers respectively. All these gaps have similarvalues in a one-to-one corresponding way. For example, the gaps 311,331, and 351 are of similar value.

As illustrated in FIG. 2(d), the metal contacts 307, 305, 303, and 301are all of a rectangle shape. The metal contacts 305, 303, and 301 areof a rectangle shape with a substantially similar length which is lessthan a length of the top metal contact 307, and with a substantiallysimilar width which is less than a width of the top metal contact 307.For example, the top metal contact 307 may be of a rectangle shape witha length from about 30 μm to about 200 μm and a width from about 30 μmto about 100 μm, while other metal contacts 305, 303, and 301 may be ofa rectangle shape with a substantially similar length from about 20 μmto about 190 μm, and with a substantially similar width from about 20 μmto about 90 μm.

FIG. 2(e) illustrates a cross-section view of the metal contacts 301,303, 305, and 307 and contact pad 501 shown in FIG. 2(d), in addition tothe passivation layer 502 and the dielectric layer 504. The top metalcontact 307 is substantially overlapped with the projected image of thecontact pad 501 projected onto the top metal layer. The metal contacts305, 305, and 301 are of substantially similar length as shown in FIG.2(d). The distance 351 corresponds to the gap 351 shown in FIG. 2(d)between an edge of the projected image of the top metal contact 307 andan edge of the metal contact 305. Similarly, the distance 353corresponds to another gap 353 in FIG. 2(d). The two distances 351 and353 on the two sides of the metal contact 305 may be of a similar value,or may be of a different value. Other distances 331, 333, 311, and 313are similarly described and correspond to the gaps 331, 333, 311, and313 in FIG. 2(d).

FIGS. 3(a)-3(e) illustrate various additional embodiments of theformation of a plurality of metal contacts under the ground-up contactpad 501.

FIG. 3(a) is the same as the FIG. 2(e) in cross-section view. All themiddle metal contacts 305, 303 at the middle metal layers and the bottommetal contact 301 are of a rectangle shape with substantially similarlength and width. Furthermore, they are substantially overlapped atdifferent layers, and are all strictly smaller than the top metalcontact 307.

Alternatively as shown in FIG. 3(b), the middle metal contact 305 issubstantially overlapped with the top metal contact 307 at differentlayers, while the middle metal contact 303 is substantially overlappedwith the bottom contact 301 at different layers.

Alternatively as shown in FIG. 3(c), the top metal contact 307 isstrictly larger than the metal contact 305 substantially vertically nextbelow the top metal contact 307. The metal contact 305 is strictlylarger than the metal contact 303 substantially vertically next belowthe metal contact 305. The metal contact 303 is strictly larger than themetal contact 301 substantially vertically next below the metal contact303. In general, if there are multiple middle metal layers, then for anygiven metal layer of the multiple middle metal layers, the metal contactin the given metal layer may be strictly larger than a metal contactsubstantially vertically next below the metal contact.

The metal contacts 307, 305, 303, and 301 shown in FIGS. 3(a)-3(c) areall of a rectangle shape. Other shapes of metal contacts are possible.As illustrated in FIG. 3(d), the metal contacts 305, 303, and 301 are ofa circular shape while the top metal contact 307 and the contact pad 501are of a rectangle shape. It may be advantageous to have the top metalcontact 307 and the contact pad 501 to be of a same or similar shape.Furthermore, as shown in FIG. 3(e), the metal contact 303 is a rectangleand the metal contacts 305 and 301 are circles. There may be many otherways to mix the shapes of the middle metal contacts and the bottom metalcontacts. In FIGS. 3(d)-3(e), the top metal contact 307 is strictlylarger than the metal contact 305 substantially vertically next belowthe top metal contact 307. The metal contact 305 is strictly larger thanthe metal contact 303 substantially vertically next below the metalcontact 305. The metal contact 303 is strictly larger than the metalcontact 301 substantially vertically next below the metal contact 303.

FIGS. 4(a)-4(c) illustrate further additional embodiments of theformation of a plurality of metal layers 101, 103, 105, and 107 under aground-up contact pad 501, where a metal layer may comprise multiplemetal contacts.

FIG. 4(a) illustrates an embodiment where there is a plurality of metalcontacts 3051, 3053 at the middle metal layer 105, which are allsubstantially vertically below the metal contact 307, which is the metalcontact at a layer immediately above the middle metal layer 105.Alternatively, there may be even more metal contacts in a metal layersuch as the six metal contacts in the metal layer 105 and the metallayer 103 shown in FIG. 4(b) in a top view.

As illustrated in FIG. 4(a), for any metal layers below the metal layer105, there is a plurality of metal contacts at each layer as well. Forexample, the two metal contacts 3031 and 3033 are at the middle metallayer 103 below the metal layer 105, and the two metal contacts 3011 and3013 are at the bottom metal layer 101. Furthermore, the metal contact3011 is substantially vertically below the metal contact 3031, which isfurther substantially vertically below the metal contact 3051.Similarly, the metal contact 3013 is substantially vertically below themetal contact 3033, which is further substantially vertically below themetal contact 3053. In general, any metal contact below the metal layer105 is substantially vertically below one of the plurality of metalcontacts of the metal layer 105.

The multiple metal contacts shown in FIGS. 4(a)-4(b) at layers 105, 103,and 101 are of substantially similar size and substantially overlappedwith other metal contacts at different layers. Alternatively, themultiple metal contacts at one layer can be of different sizes from themultiple metal contacts at a different layer. As shown in FIG. 4(c), themiddle metal layer 105 may still comprise one metal contact 305substantially vertically below the top metal contact 307. The middlemetal layer 103 may comprise a plurality of metal contacts 3031 and3033, and the bottom metal layer 101 may comprise a plurality of bottommetal contacts 3011 and 3013. The bottom metal contact 3011 issubstantially vertically below and strictly smaller than the metalcontact 3031. The bottom metal contact 3013 is substantially verticallybelow and strictly smaller than the metal contact 3033.

According to an embodiment, a device includes a bottom metal layer, thebottom metal layer comprising a bottom metal contact, a top metal layerabove the bottom metal layer, the top metal layer comprising a top metalcontact, and a contact pad substantially vertically above the top metalcontact, a major surface of the contact pad physically contacting amajor surface of the top metal contact. The device further includes afirst middle metal layer between the top metal layer and the bottommetal layer, the first middle metal layer comprising a plurality offirst middle metal contacts, wherein the plurality of first middle metalcontacts are disposed vertically below and within a lateral extent ofthe contact pad, wherein the contact pad and the top metal contact havea same size and shape in a plan view, and wherein each of the bottommetal contact and the plurality of first middle metal contacts has ashorter length and a shorter width than a length and a width of the topmetal contact.

According to another embodiment, a device includes a bottom metal layer,the bottom metal layer comprising a bottom metal contact, a first middlemetal layer above the bottom metal layer, the first middle metal layercomprising a plurality of first middle metal contacts, and a top metallayer above the first middle metal layer, the top metal layer comprisinga top metal contact above the plurality of first middle metal contacts.The device further includes a contact pad above the top metal contact, abottom surface of the contact pad being in physical contact with the topmetal contact, wherein the plurality of first middle metal contacts aredisposed below and within a lateral extent of the contact pad, whereinthe contact pad and the top metal contact have a same size and shape ina plan view, wherein each of the plurality of first middle metalcontacts is smaller in all dimensions than the contact pad in the planview, and wherein the bottom metal contact is smaller in all dimensionsthan each of the plurality of first middle metal contacts in the planview.

According to yet another embodiment, a device includes a bottom metallayer, the bottom metal layer comprising a bottom metal contact, a topmetal layer over the bottom metal layer, the top metal layer comprisinga top metal contact, and a contact pad over the top metal contact, amajor surface of the contact pad being in physical contact with a majorsurface of the top metal contact. The device further includes a middlemetal layer between the bottom metal layer and the top metal layer, themiddle metal layer comprising a middle metal contact, wherein the middlemetal contact and the bottom metal contact are disposed vertically belowand within a perimeter of the contact pad in a plan view, wherein thecontact pad and the top metal contact have a same size and shape in theplan view, wherein the middle metal contact is smaller in all dimensionsthan the contact pad in the plan view, and wherein the bottom metalcontact is smaller in all dimensions than the middle metal contact inthe plan view.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps. In addition, eachclaim constitutes a separate embodiment, and the combination of variousclaims and embodiments are within the scope of the invention.

What is claimed is:
 1. A device comprising: a bottom metal layer, thebottom metal layer comprising a bottom metal contact; a top metal layerabove the bottom metal layer, the top metal layer comprising a top metalcontact; a contact pad substantially vertically above the top metalcontact, a major surface of the contact pad physically contacting amajor surface of the top metal contact; and a first middle metal layerbetween the top metal layer and the bottom metal layer, the first middlemetal layer comprising a plurality of first middle metal contacts,wherein the plurality of first middle metal contacts are disposedvertically below and within a lateral extent of the contact pad, whereinthe contact pad and the top metal contact have a same size and shape ina plan view, and wherein each of the bottom metal contact and theplurality of first middle metal contacts has a shorter length and ashorter width than a length and a width of the top metal contact in theplan view.
 2. The device of claim 1, further comprising a second middlemetal layer between the top metal layer and the first middle metallayer, the second middle metal layer comprising a second middle metalcontact.
 3. The device of claim 2, wherein the contact pad and thesecond middle metal layer have a same size and shape in the plan view.4. The device of claim 2, further comprising a plurality of first viasbetween the top metal layer and the second middle metal layer.
 5. Thedevice of claim 4, further comprising: a plurality of second viasbetween the first middle metal layer and the second middle metal layer;and a plurality of third vias between the first middle metal layer andthe bottom metal layer, the plurality of second vias and the pluralityof third vias being aligned.
 6. The device of claim 1, wherein thecontact pad has a thickness between 0.5 μm and about ₄ μm.
 7. The deviceof claim 1, wherein the top metal contact has a rectangular shape with alength from about 30 μm to about 200 μm and a width from about 30 μm toabout 100 μm.
 8. A device comprising: a bottom metal layer, the bottommetal layer comprising a bottom metal contact; a first middle metallayer above the bottom metal layer, the first middle metal layercomprising a plurality of first middle metal contacts; a top metal layerabove the first middle metal layer, the top metal layer comprising a topmetal contact above the plurality of first middle metal contacts; and acontact pad above the top metal contact, a bottom surface of the contactpad being in physical contact with the top metal contact, wherein theplurality of first middle metal contacts are disposed below and within alateral extent of the contact pad, wherein the contact pad and the topmetal contact have a same size and shape in a plan view, wherein each ofthe plurality of first middle metal contacts is smaller in alldimensions than the contact pad in the plan view, and wherein the bottommetal contact is smaller in all dimensions than each of the plurality offirst middle metal contacts in the plan view.
 9. The device of claim 8,a second middle metal layer between the top metal layer and the firstmiddle metal layer, the second middle metal layer comprising a secondmiddle metal contact.
 10. The device of claim 9, wherein the contact padand the second middle metal contact have a same size and shape in theplan view.
 11. The device of claim 9, further comprising: a plurality offirst vias electrically coupling the first middle metal layer to thesecond middle metal layer; and a plurality of second vias electricallycoupling the first middle metal layer to the bottom metal layer by, theplurality of first vias being vertically aligned with the plurality ofsecond vias.
 12. The device of claim 11, further comprising a pluralityof third vias electrically coupling the top metal layer to the secondmiddle metal layer.
 13. The device of claim 8, further comprising apassivation layer over the top metal layer, the contact pad extendinginto the passivation layer.
 14. The device of claim 13, furthercomprising a polymer layer over the passivation layer, the polymer layerextending along a top surface of the contact pad.
 15. A devicecomprising: a bottom metal layer, the bottom metal layer comprising abottom metal contact; a top metal layer over the bottom metal layer, thetop metal layer comprising a top metal contact; a contact pad over thetop metal contact, a major surface of the contact pad being in physicalcontact with a major surface of the top metal contact; and a middlemetal layer between the bottom metal layer and the top metal layer, themiddle metal layer comprising a middle metal contact, wherein the middlemetal contact and the bottom metal contact are disposed vertically belowand within a perimeter of the contact pad in a plan view, wherein thecontact pad and the top metal contact have a same size and shape in theplan view, wherein the middle metal contact is smaller in all dimensionsthan the contact pad in the plan view, and wherein the bottom metalcontact is smaller in all dimensions than the middle metal contact inthe plan view.
 16. The device of claim 15, further comprising: aplurality of first vias electrically coupling the middle metal contactto the top metal contact; and a plurality of second vias electricallycoupling the middle metal contact to the bottom metal contact, theplurality of first vias being vertically aligned with the plurality ofsecond vias.
 17. The device of claim 15, wherein the middle metalcontact has a first plan-view shape, wherein the bottom metal contacthas a second plan-view shape, and wherein the first plan-view shape isdifferent from the second plan-view shape.
 18. The device of claim 15,wherein the middle metal contact has a first plan-view shape, whereinthe bottom metal contact has a second plan-view shape, and wherein thefirst plan-view shape is same as the second plan-view shape.
 19. Thedevice of claim 15, wherein the middle metal contact is within theperimeter of the top metal contact in the plan view.
 20. The device ofclaim 15, wherein the bottom metal contact is within the perimeter ofthe top metal contact in the plan view.